In many consumer packaging applications, it is important to prevent air or water from passing out of or into a package containing certain products. This is particularly true with respect to meat packages, cheese packages, and the like, for which the contained product must be kept in a constant environment to prevent spoilage. In order to preserve the product contained within such a package, the periphery of the package must be hermetically sealed. Hermetic seals can be provided by both permanent seals and temporary seals, known as peelable seals. Peelable seals are usable to provide a hermetic seal and, at the same time, provide a consumer with access to the contents of the package. A consumer breaks a peelable seal of a package by first grabbing onto opposing film faces to which peelable seal materials are adhered and then pulling the film faces apart.
A common method of packaging foods, such as sliced luncheon meats and the like, is by use of a horizontal form, fill, and seal procedure. These procedures involve shaping a portion of film ("form"), placing the food article inside or upon the formed film portion ("fill"), completing the closure of the film portion around the food article and "sealing" open edges to complete the packaging process.
In some implementations, one sealing station is used to seal all the edges of a package and, at the same time, make a peelable seal from a strip of peelable materials. The "sealing" stage of the form, fill, and seal procedure often involves using a resealable closure mechanism. The resealable closure mechanism and peelable seal are often produced as separate items from the package and are attached to and made integral with the package at a later point in the manufacturing process by a heat and pressure sealing process. In most implementations, the packages are made of polymeric materials, because these materials inhibit the migration of air and water from and into the package.
To provide a peelable seal on a package with a resealable closure mechanism, the package typically uses permanent seals at its side edges and bottom edge and a peelable seal above or below the resealable closure mechanism at the mouth end of the package. In addition, the peelable seal may be arranged on either the flange/base portions of the closure mechanism or on the packaging film adjacent to the flange portions.
The strength of the peelable seal is determined by the composition of the peelable material, temperature, pressure, dwell time of the seal bars, and the size of the peelable seal. The peelable seal needs to be strong enough to provide an adequate hermetic seal, but weak enough to allow the consumer to "peel" the peelable seal apart. Peelable seals are highly susceptible to small variations that might occur during manufacturing; i.e., the peelable seals have low manufacturing tolerances. Given these manufacturing variations, it is difficult to control the strength of the peelable seal.